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<chapter xml:id="mail"

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<title>Email</title>

<section xml:id="mail-introduction">

<title>Introduction</title>

<sidebar>

<title>Library dependencies</title>

<para>The following additional jars to be on the classpath of your

application in order to be able to use the Spring Framework's email library.</para>

<itemizedlist>

<listitem>

<para>The <link xl:href="http://java.sun.com/products/javamail/">JavaMail</link> <filename class="libraryfile">mail.jar</filename> library</para>

</listitem>

<listitem>

<para>The <link xl:href="http://java.sun.com/products/javabeans/jaf/downloads/index.html">JAF</link> <filename class="libraryfile">activation.jar</filename> library</para>

</listitem>

</itemizedlist>

<para>All of these libraries are freely available on the web.</para>

</sidebar>

<para>The Spring Framework provides a helpful utility library for sending

email that shields the user from the specifics of the underlying mailing

system and is responsible for low level resource handling on behalf of

the client.</para>

<para>The <literal>org.springframework.mail</literal> package is the root level package

for the Spring Framework's email support. The central interface for sending

emails is the <interfacename>MailSender</interfacename> interface; a simple value object

encapsulating the properties of a simple mail such as <emphasis>from</emphasis> and

<emphasis>to</emphasis> (plus many others) is the <classname>SimpleMailMessage</classname> class.

This package also contains a hierarchy of checked exceptions which provide

a higher level of abstraction over the lower level mail system exceptions

with the root exception being <exceptionname>MailException</exceptionname>. Please

refer to the JavaDocs for more information on the rich mail exception hierarchy.</para>

<para>The <interfacename>org.springframework.mail.javamail.JavaMailSender</interfacename>

interface adds specialized <emphasis>JavaMail</emphasis> features such as MIME

message support to the <interfacename>MailSender</interfacename> interface

(from which it inherits). <interfacename>JavaMailSender</interfacename> also provides a

callback interface for preparation of JavaMail MIME messages, called

<interfacename>org.springframework.mail.javamail.MimeMessagePreparator</interfacename></para>

</section>

<section xml:id="mail-usage">

<title>Usage</title>

<para>Let's assume there is a business interface called <interfacename>OrderManager</interfacename>:</para>

<programlisting language="java"><![CDATA[public interface OrderManager {

}]]></programlisting>

<para>Let us also assume that there is a requirement stating that an email message

with an order number needs to be generated and sent to a customer placing the

relevant order.</para>

<section xml:id="mail-usage-simple">

<title>Basic <interfacename>MailSender</interfacename> and <classname>SimpleMailMessage</classname> usage</title>

<programlisting language="java"><![CDATA[import org.springframework.mail.MailException;

]]><lineannotation>// Do the business calculations...</lineannotation><![CDATA[

]]><lineannotation>// Call the collaborators to persist the order...</lineannotation><![CDATA[

]]><lineannotation>// Create a thread safe "copy" of the template message and customize it</lineannotation><![CDATA[

]]><lineannotation>// simply log it and go on...</lineannotation><![CDATA[

}]]></programlisting>

<para>Find below the bean definitions for the above code:</para>

<programlisting language="xml"><![CDATA[<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">

]]><lineannotation>&lt;!-- this is a template message that we can pre-load with default state --&gt;</lineannotation><![CDATA[

</bean>]]></programlisting>

</section>

<section xml:id="mail-usage-mime">

<title>Using the <interfacename>JavaMailSender</interfacename> and the <classname>MimeMessagePreparator</classname></title>

<para>Here is another implementation of <interfacename>OrderManager</interfacename> using

the <interfacename>MimeMessagePreparator</interfacename> callback interface. Please note

in this case that the <literal>mailSender</literal> property is of type

<interfacename>JavaMailSender</interfacename> so that we are able to use the JavaMail

<classname>MimeMessage</classname> class:</para>

<programlisting language="java"><![CDATA[import javax.mail.Message;

]]><lineannotation>// Do the business calculations...</lineannotation><![CDATA[

]]><lineannotation>// Call the collaborators to persist the order...</lineannotation><![CDATA[

]]><lineannotation>// simply log it and go on...</lineannotation><![CDATA[

}]]></programlisting>

<note>

<para>The mail code is a crosscutting concern and could well be a candidate

for refactoring into a <link linkend="aop">custom Spring AOP aspect</link>,

which then could be executed at appropriate joinpoints on the

<interfacename>OrderManager</interfacename> target.</para>

</note>

<para>The Spring Framework's mail support ships with the standard JavaMail

implementation. Please refer to the relevant JavaDocs for more information.</para>

</section>

</section>

<section xml:id="mail-javamail-mime">

<title>Using the JavaMail <classname>MimeMessageHelper</classname></title>

<para>A class that comes in pretty handy when dealing with JavaMail messages is

the <classname>org.springframework.mail.javamail.MimeMessageHelper</classname> class,

which shields you from having to use the verbose JavaMail API. Using

the <classname>MimeMessageHelper</classname> it is pretty easy to

create a <classname>MimeMessage</classname>:</para>

<programlisting language="java"><lineannotation>// of course you would use DI in any real-world cases</lineannotation><![CDATA[

sender.send(message);]]></programlisting>

<section xml:id="mail-javamail-mime-attachments">

<title>Sending attachments and inline resources</title>

<para>Multipart email messages allow for both attachments and inline resources.

Examples of inline resources would be images or a stylesheet you want to use

in your message, but that you don't want displayed as an attachment.</para>

<section xml:id="mail-javamail-mime-attachments-attachment">

<title>Attachments</title>

<para>The following example shows you how to use the

<classname>MimeMessageHelper</classname> to send an email along with a

single JPEG image attachment.</para>

<programlisting language="java"><![CDATA[JavaMailSenderImpl sender = new JavaMailSenderImpl();

]]><lineannotation>// use the true flag to indicate you need a multipart message</lineannotation><![CDATA[

]]><lineannotation>// let's attach the infamous windows Sample file (this time copied to c:/)</lineannotation><![CDATA[

sender.send(message);]]></programlisting>

</section>

<section xml:id="mail-javamail-mime-attachments-inline">

<title>Inline resources</title>

<para>The following example shows you how to use the

<classname>MimeMessageHelper</classname> to send an email along with an

inline image.</para>

<programlisting language="java"><![CDATA[JavaMailSenderImpl sender = new JavaMailSenderImpl();

]]><lineannotation>// use the true flag to indicate you need a multipart message</lineannotation><![CDATA[

]]><lineannotation>// use the true flag to indicate the text included is HTML</lineannotation><![CDATA[

]]><lineannotation>// let's include the infamous windows Sample file (this time copied to c:/)</lineannotation><![CDATA[

sender.send(message);]]></programlisting>

<warning>

<para>Inline resources are added to the mime message using the

specified <literal>Content-ID</literal> (<literal>identifier1234</literal>

in the above example). The order in which you are adding the text and the

resource are <emphasis role="bold">very</emphasis> important. Be sure to

<emphasis>first add the text</emphasis> and after that the resources. If

you are doing it the other way around, it won't work!</para>

</warning>

</section>

</section>

<section xml:id="mail-templates">

<title>Creating email content using a templating library</title>

<para>The code in the previous examples explicitly created the

content of the email message, using methods calls such as

<methodname>message.setText(..)</methodname>. This is fine for

simple cases, and it is okay in the context of the aforementioned

examples, where the intent was to show you the very basics of the API.</para>

<para>In your typical enterprise application though, you are not going

to create the content of your emails using the above approach for a number

of reasons.</para>

<para>

<itemizedlist>

<listitem>

<para>Creating HTML-based email content in Java code is tedious and error prone</para>

</listitem>

<listitem>

<para>There is no clear separation between display logic and business logic</para>

</listitem>

<listitem>

<para>Changing the display structure of the email content requires writing Java code, recompiling, redeploying...</para>

</listitem>

</itemizedlist>

</para>

<para>Typically the approach taken to address these issues is to use a template library

such as FreeMarker or Velocity to define the display structure of email content. This leaves

your code tasked only with creating the data that is to be rendered in the email

template and sending the email. It is definitely a best practice for when

the content of your emails becomes even moderately complex, and with

the Spring Framework's support classes for FreeMarker and Velocity becomes

quite easy to do. Find below an example of using the Velocity template library

to create email content.</para>

<section xml:id="mail-templates-example">

<title>A Velocity-based example</title>

<para>To use <link xl:href="http://velocity.apache.org">Velocity</link> to

create your email template(s), you will need to have the Velocity libraries

available on your classpath. You will also need to create one or more Velocity templates

for the email content that your application needs. Find below the Velocity

template that this example will be using. As you can see it is HTML-based,

and since it is plain text it can be created using your favorite HTML

or text editor.</para>

<programlisting language="xml"><lineannotation># in the com/foo/package</lineannotation><![CDATA[

</html>]]></programlisting>

<para>Find below some simple code and Spring XML configuration that

makes use of the above Velocity template to create email content and

send email(s).</para>

<programlisting language="java"><![CDATA[package com.foo;

]]><lineannotation>// Do the registration logic...</lineannotation><![CDATA[

message.setFrom("webmaster@csonth.gov.uk"); ]]><lineannotation>// could be parameterized...</lineannotation><![CDATA[

}]]></programlisting>

<programlisting language="xml"><![CDATA[<?xml version="1.0" encoding="UTF-8"?>

</beans>]]></programlisting>

</section>

</section>

</section>

</chapter>